| 摘要 |
PURPOSE:To prevent flicker without influenced by temperature characteristic and secular change by controlling a gain automatically by the difference in peak value between even number field and odd number field, and controlling a pedestal level by the average value of each horizontal period. CONSTITUTION:The same reproduced field signal 17 is converted to a frame signal, by selecting alternately field signals of 0.5H delay and a through signal by a switch 16 every one vertical scanning period. The converted frame signal is switch-controlled by switch controlling pulse 35 and an inverter 36 and inputted to a peak detectors 27, 28, and, for instance, the difference in peak value between even number field and odd number field is detected and an automatic gain controller 24 is controlled by the difference signal. The pedestal level of each horizontal scanning period is sampled by a switch 31, averaged by an integrating circuit 32 and clamping circuits 33, 34 are controlled. In such a way, flicker can be prevented without influenced by temperature characteristic and secular change. |
